“The term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the poles, the National Weather Service said on its website, but when it strays south, it can cause brutal weather conditions in the U.S., including sub-zero temperatures.

In the winter, the polar vortex expands or migrates, which happens fairly regularly, and forces frigid air southward. Parts of the system have even reached as far south as Florida in years past, NOAA officials said.